Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana

ERASMUS MUNDUS MSC PROGRAMME COASTAL AND MARINE ENGINEERING AND MANAGEMENT COMEM MODELING THE EVOLUTION OF THE WAX LAKE DELTA IN ATCHAFALAYA BAY, LOUISIANA Delft University of Technology June 2011 Kevin Hanegan 4055284 The Erasmus Mundus MSc Coastal and Marine Engineering and Management is an integrated programme organized by five European partner institutions, coordinated by Delft University of Technology (TU Delft). The joint study programme of 120 ECTS credits (two years full-time) has been obtained at three of the five CoMEM partner institutions: Norges Teknisk- Naturvitenskapelige Universitet (NTNU) Trondheim, Norway Technische Universiteit (TU) Delft, The Netherlands City University London, Great Britain Universitat Politècnica de Catalunya (UPC), Barcelona, Spain University of Southampton, Southampton, Great Britain The first year consists of the first and second semesters of 30 ECTS each, spent at NTNU, Trondheim and Delft University of Technology respectively. The second year allows for specialization in three subjects and during the third semester courses are taken with a focus on advanced topics in the selected area of specialization: Engineering Management Environment In the fourth and final semester an MSc project and thesis have to be completed. The two year CoMEM programme leads to three officially recognized MSc diploma certificates. These will be issued by the three universities which have been attended by the student. The transcripts issued with the MSc Diploma Certificate of each university include grades/marks for each subject. A complete overview of subjects and ECTS credits is included in the Diploma Supplement, as received from the CoMEM coordinating university, Delft University of Technology (TU Delft). Information regarding the CoMEM programme can be obtained from the programme coordinator and director Prof. Dr. Ir. Marcel J.F. Stive Delft University of Technology Faculty of Civil Engineering and geosciences P.O. Box 5048 2600 GA Delft The Netherlands Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana Kevin C. Hanegan A thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering within the Coastal and Marine Engineering and Management (CoMEM) program Delft University of Technology Delft, the Netherlands Submitted for approval on June 27, 2011 Graduation Committee: Prof.dr.ir. M.J.F. Stive Delft University of Technology (Chairman) Ir. A.P. Luijendijk Delft University of Technology/Deltares Dr. J.E.A. Storms Delft University of Technology Drs. N. Geleynse Delft University of Technology Dr.ir. M. van Ledden Royal Haskoning Ir. T. M. Kluyver Royal Haskoning Ir. M. M. Hillen Royal Haskoning Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana June 2011 Preface This thesis represents the conclusion of my MSc work in the Coastal and Marine Engineering and Management program where I studied at the Norwegian University of Science and Technology, the Universitat Politecnica de Catalunya, and Delft University of Technology. I’d like to thank the organizing universities, professors, and CoMEM board for giving us all such a great opportunity to learn coastal engineering in the varying cultures and contexts within Europe, as well as the other CoMEM students who have helped to make it such a great experience. The majority of this research was carried out with Haskoning, Inc. in New Orleans, Louisiana. I really appreciated the opportunity to live and work in such an interesting place and the great support that I received from everyone there, and thank Professor Stive, Mathijs van Ledden, Maarten Kluyver, and everyone else at Haskoning who made the research possible. It was a pleasure to work with my Dutch colleagues Maarten, Reis, and Martje and fellow students Matthijs and Alissa in New Orleans. Special thanks to my advisors who offered wonderful guidance despite my being so far away. Nathanael Geleynse and Marten Hillen were especially helpful with particular modeling questions, and in New Orleans, Maarten Kluyver helped to keep the work on track with frequent discussions and review despite his busy schedule. I want to thank Ioannis Giorgiou of the University of New Orleans, who provided both computer resources and substantial guidance on model development. His expertise on Louisiana coastal processes was very valuable, and the work could not have been completed without his help. Also, I’d like to thank Steve Ayers and others at the USACE New Orleans District who helped with tracking down bathymetry data sets. I’d like to acknowledge the help of my former professor Dr. Clint Willson and colleagues at LSU in developing the initial study idea, and the substantial work by Harry Roberts and others at the Coastal Studies Institute from which any study of the Louisiana Coast and deltaic processes proceeds. Lastly, I’d like to thank my family for their continued support and for all the opportunities I have had because of their hard work, and especially Hannah for all her support, patience, help, and understanding during the research and throughout my MSc program. Kevin Hanegan Delft 2011 i June 2011 Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana ii Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana June 2011 Abstract In this study, a process-based, depth-averaged Delft3D hydrodynamic and morphologic model of the Wax Lake Delta in Atchafalaya Bay, Louisiana was developed to simulate a five year period of delta development from the beginning of 1998 to the end of 2002. The purpose of this modeling effort was to test the ability of process-based modeling tools to successfully simulate typical delta-building processes and the resulting morphologic and stratigraphic characteristics of the delta. Recent developments in conceptual modeling of mouth bar formation and full delta development have confirmed the capability of process-based models to simulate the processes necessary for delta growth and the resulting long-term, geologic scale morphologic and stratigraphic features. In this attempt to model the actual development of a prototype delta using similar techniques to those employed in the conceptual delta models, the applicability of physics-based modeling to delta evolution simulation will be further validated. Initial model bathymetry was obtained from the grid of a USACE hydrodynamic model of the study area based on 1998 hydrographic surveys augmented with LIDAR survey data for overbank areas. The Wax Lake Delta morphology has been primarily shaped by river mouth processes, where mouth bar formation induces channel bifurcation and further basinward progradation. Because of the Wax Lake Delta river-dominance, marine processes including wave action, tidal oscillation, and wind induced water level changes and currents were neglected in the model. Variation of grain sizes in the bed composition and suspended sediment load was represented by a fine-sand non-cohesive fraction and a cohesive mud fraction. To represent the strong seasonal variation in discharge and sediment transport through the Wax Lake Outlet, the upstream boundary discharge regime was schematized into four periods of constant discharge representative of low flows, the annual flood, the 2-year flood, and the 5-year flood magnitude, with proportion of occurrence during each morphological year assigned based on a sediment transport-scaled frequency-duration curve. Corresponding inflow concentrations for the two sediment fractions were calculated from functional relationships to discharge derived from long-term concurrent measurements at the model upstream boundary. Hydrodynamics and transport were calibrated using measurements of velocity and sediment concentration across multiple transects of delta distributary channels taken during a single flood-condition event. The calibrated model was then used along with the schematized boundary conditions to simulate a five year period of long-term morphological development. Morphology qualitatively reproduced typical river-dominant delta growth through the establishment of new depositional lobes while maintaining approximate radial symmetry. More specific stratigraphic features were also reproduced. The successive stacking of coarsening upwards sequences observed in Wax Lake Delta mouth bar deposits was evident in the stratigraphy of modeled incipient jet deposits, a result of the varying discharge regime. Though incipient jet deposits developed in the model at the distal ends of distributary channels, the prograding bars did not aggrade sufficiently to induce flow bifurcation and the development of a mature mouth bar depositional lobe. The lack of full mouth bar development could be a consequence of altered jet structure with the extreme channel incision and narrowing, a reduced sediment supply as the full 10 m thick bed is eroded upstream, and a non-representative initial bathymetry that does not capture the already-developing mouth bar deposit. The overall coarsening-upwards, though sand dominant stratigraphic sequence of typical friction-dominant river mouth deposits is reproduced. Significant mud-dominant prodelta deposition is observed basinward of the original delta front location. In the iii June 2011 Modeling the Evolution of the Wax Lake Delta in Atchafalaya Bay, Louisiana prototype Wax Lake Delta, deposition of fine sediments in this area is hindered by waves and wind- induced transport, so the modeled mud depositional bodies do not reflect prototype

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